Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.89   10.612%   $59.6088   $59.61   $59.60   $59.60  
  Purchase #2 $114.95   9.637%   $126.0277   $126.03   $126.05   $126.00  
  Purchase #3 $122.68   5.503%   $129.4311   $129.43   $129.45   $129.40  
  Purchase #4 $34.30   11.781%   $38.3409   $38.34   $38.35   $38.30  
  Purchase #5 $124.52   7.413%   $133.7507   $133.75   $133.75   $133.80  
  Purchase #6 $240.27   3.284%   $248.1605   $248.16   $248.15   $248.20  
  Purchase #7 $81.65   8.320%   $88.4433   $88.44   $88.45   $88.40  
  7 purchase totals = $772.26       $823.7630   $823.76   $823.80   $823.70